The present invention is directed toward an improved technique for effecting the catalytic conversion of a hydrocarbonaceous reactant stream in a multiple-stage reaction system wherein (i) the reactant stream flows serially through the plurality of reaction zones and, (ii) the catalyst particles are movable through each reaction zone via gravity-flow. More particularly, the described technique is adaptable for utilization in vapor-phase systems wherein the conversion reactions are principally endothermic, and where the flow of the hydrocarbonaceous reactant stream, with respect to the downward direction of catalyst particle movement, is cocurrent and essentially radial.
Various types of multiple-stage reaction systems have found widespread utilization throughout the petroleum and petrochemical industries for effecting multitudinous reactions, especially hydrocarbon conversion reactions. Such reactions are either exothermic, or endothermic, and encompass both hydrogen-producing and hydrogen-consuming processes. Multiple-stage reaction systems generally take one of two forms: (1) side-by-side configuration with intermediate heating between the reaction zones, and wherein the reactant stream or mixture flows serially from one zone to another zone; and, (2) a stacked design wherein a single reaction chamber, or more, contains the multiple catalytic contact stages. Such reactor systems, as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversion reactions including those which predominate in catalytic reforming, alkylation, ethylbenzene dehydrogenation to produce styrene, other dehydrogenation processes, etc. Our invention is capable of utilization in those processes where the conversion reactions are effected in vapor-phase and catalyst particles are movable via gravity-flow, and where the reaction system exists in side-by-side relation, where two or more reaction zones are vertically aligned, where one or more additional reaction zones, either in side-by-side or vertically aligned configuration, are disposed in a side-by-side relationship with two or more vertically aligned reaction zones, or where all reaction zones are in side-by-side relation.
Since catalyst particles which are movable through a reaction system by way of gravity-flow are necessarily moving in a downward direction, the present technique contemplates the withdrawal of catalyst particles from a bottom portion of one reaction zone and the introduction of fresh, or regenerated catalyst particles into the top portion of the same or a second reaction zone. The present technique is also intended to be applied to those reaction systems wherein the catalyst is disposed as an annular bed and the flow of the reactant stream across the bed is radial.
A radial-flow reaction system generally consists of tubular-form sections, having varying nominal cross-sectional areas, vertically and coaxially disposed to form the reaction vessel. Briefly, the system comprises a reaction chamber containing a coaxially disposed catalyst-retaining screen, said screen having a nominal, internal cross-sectional area less than said chamber, and a perforated centerpipe having a nominal, internal cross-sectional area which is less than the catalyst-retaining screen. The reactant stream may be introduced, in vapor-phase, into the annular-form space created between the inside wall of the chamber and the outside surface of the catalyst-retaining screen. The latter forms an annular-form, catalyst-holding zone with the outside surface of the perforated centerpipe; vaporous reactant flows laterally and radially inward through the screen and catalyst zone into the centerpipe and out of the reaction chamber. Alternatively the reactant stream may be introduced into the perforated centerpipe where it flows laterally and radially outward through the centerpipe, catalyst zone and catalyst-retaining screen and into the annular-form space created between the inside wall of the chamber and the outside surface of the catalyst-retaining screen where it leaves the reaction chamber. Although the tubular-form configuration of the various reactor components may take any suitable shape--e.g. triangular, square, oblong, diamond, etc., many design, fabrication and technical considerations dictate the advantages of using components which are substantially circular in cross-section and one such particularly preferred configuration comprises a group of scalloped-shaped elements fabricated into a circular-form screen as disclosed in U.S. Pat. No. 2,683,654.
Illustrative of a multiple-stage stacked reactor system, having gravity-flowing catalyst particles, and to which the present invention is particularly adaptable, is that shown in U.S. Pat. No. 3,706,536. Transfer of the gravity-flowing catalyst particles, from one reaction zone to another, as well as introduction of fresh catalyst particles and withdrawal of "spent" catalyst particles, is effected through the utilization of a plurality of catalyst-transfer conduits. Deactivated catalyst particles are withdrawn from the last reaction zone and transferred to a regenerating tower through which they are also downwardly movable via gravity-flow.
It is to such systems, as well as those hereafter discussed as being illustrative of the current known state of the art, that the present invention is intended to be most appropriately applicable. Briefly, our inventive concept encompasses a process wherein two separate reactor systems, each of which contains from one to three individual reaction zones, share a comnon catalyst regenerating tower. Each system contains a different catalytic composite having different activity, stability and/or selectivity characteristics than the composite in the other system. More specifically, the process herein described is of special advantage when utilized in the catalytic reforming of a hydrocarbonaceous charge stock for the production of high yields of a high octane blending value normally liquid product.